<http://www.buildinggreen.com/auth/article.cfm/2009/3/9/The-First-Practical-Heliostat/>

I thought this may be of interest.

Bruce

I've wondered by I kept seeing buckled siding in developments. "Energy Design Update reported in April 2007 on the mysterious melting of vinyl siding on homes. It turns out that reflected light, especially from low-e glass, is hot enough to distort or melt PVC; the problem can be exacerbated if the glass deflects when heated up, becoming concave. "

No doubt. The reflection off of the windows in my Colorado house is literally cooking the redwood deck in front of them. When I've cleaned the wood(prior to staining) it smells like charcoal. Of course, the sun is particularly powerful at high elevations in Colorado.

With energy efficient houses reducing the size of windows (especially on the north side), this sounds like a great solution for getting lots of light and heat through a small window. Plus the angle into the house is usually horizontal or slightly upward, so the light can penetrate deeply into the house.

It is my understanding that single flat reflectors always produce less heating than direct sun. So you need multiple reflectors or concave reflectors to be a real problem.